A liquid crystal display (LCD) device which has a back light provided with light sources of a plurality of colors is known. In order to improve contrast of a video image to be displayed, to increase a color reproduction gamut and to reduce power consumption, a technique for controlling brightness and color of a light which is emitted from a backlight of an LCD device according to an input video signal is also known.
In the technique described above, the emission intensities of light sources of R (red), G (green) and B (blue) colors are set according to a maximum signal value among signal values of R, G and B color components of the input video signal. Further, the signal value to be transmitted to a liquid crystal panel is corrected considering that a light from a light source of each color is likely to leak from a liquid crystal cell of another color.
Since the technique is based on a precondition that the R, G and B color components of the input video signal correspond to the colors of the light sources in one-on-one manner respectively, the number of the colors of the light sources are limited to three of the R, G and B colors.
According to the above technique, when there is a pixel in which a certain color component has a maximum signal value, the intensity of the light source of the corresponding color is set to a maximum intensity. On the other hand, a lower limit of transmission rate of the liquid crystal panel is larger than zero. Thus, a pixel where the signal value of the color component is zero is difficult to be displayed. For example, when white (R=G=B=266) and red (R=255 and G=B=0) are simultaneously present within a screen, according to the above technique, all of the intensities of the R, G and B light sources are set to a maximum value, and all of the R, G and B signal values transmitted to the liquid crystal panel are set to a maximum value. As a result, the transmission rate becomes maximum, and “white” is accurately displayed. Since the light components of G and B are unnecessary to display red, the signal values to be transmitted to the liquid crystal panel are set to zero (G=B=0). However, since the lights of the G and B light sources leak actually, a desired red is not displayed and a color more whitish than assumed is displayed.